Electrophoresis involves the separation of charged molecular species in a molecular field. An electric field is applied to a macromolecule mixture, causing the mixture to be separated into fractions. Gel electrophoresis involves the migration of charged macromolecules through a porous gel under an applied electric field. Electrophoresis occurs because of differences in mobility of the different molecular species in the gel. Usually separation is based on differences in molecular weight, but can be based on differences in some other parameter, such as the isoelectric points of the molecular species. Gel electrophoresis may be used for either analytical or preparative purposes, and is more frequently used for the former.
Gel electrophoresis devices may be broadly categorized as vertical gel electrophoresis devices or as horizontal gel electrophoresis devices. The former have a number of advantages over the latter. This invention is concerned with vertical gel electrophoresis devices.
Representative vertical gel electrophoresis devices are shown in U.S. Pat. Nos. 4,325,796 to Hoefer et al., and 4,707,233 to Margolis. Both devices include a bottom tank and a top tank removably situated inside the bottom tank so as to provide two spaces for electrolytes, i.e., a first (or lower) space between the respective walls of the bottom and top tanks and a second (or upper) space inside the top tank. Both include a vertically extending gel receptacle or cassette which contains a gel for separation of a macromolecule mixture. In both devices, the only intended path for electricity is from an electrode in the top space or compartment to an electrode in the bottom space or compartment, via an electrolyte in the top space, the gel and an electrolyte in the bottom space, in that order.
Various problems are associated with known vertical gel electrophoresis devices. One is that most are structurally complex, and there has been an increasing tendency toward complexity with the development of the art. Another is that a tight seal must be maintained between the top and bottom compartments. This requires the use of a fluid tight gasket. Failure to maintain this tight seal may result in short circuiting, and electrolyte running out of the top compartment. Devices of both U.S. Pat. Nos. 4,325,796 and 4,707,233 require fluid tight seals between the top and bottom compartments. Some devices pose safety hazards during assembly or disassembly because both electrodes or connectors connected thereto become exposed.
Further disadvantages of the device of U.S. Pat. No. 4,325,796 include the use of clamps or screws to position the vertical gel cassettes, and a construction which makes short circuiting possible if the top compartment is overfilled with electrolyte. Adjusting clamps or screws are very undesirable because they may be overtightened, which could result in breakage of the glass forming the side walls of the cassette. Overfilling of the top compartment in this device could cause short-circuiting because of the large cross-sectional area between the respective side walls of the top and bottom tanks. If such short-circuiting should occur, the heat generated would be enough to evaporate substantial quantities of electrolyte. This could break the electrical circuit and terminate a run.
Disadvantages of the device of U.S. Pat. No. 4,707,233 include use of porous membranes in addition to the gel, and the presence of a free space between the membranes. The membranes, typically made of paper impregnated with a suitable gel, are fragile. The free recovery space provides a space in which macromolecules are collected and this space requires special efforts for cleaning. Also, both electrodes are associated with the top tank (on opposite sides of the bottom wall thereof), so that their respective connectors (not shown) could remain plugged into an external power source even after the top tank has been removed, with serious safety consequences.